This invention relates to a titania sol maintained at a stable dispersion state at a neutral pH range and a process for producing the same.
The titania sol of this invention can be adjusted to an optional pH range and furthermore finely-divided titania is maintained at a stable dispersion state in respective pH ranges. Therefore, the titania sol of this invention is suitable for various uses, for example, it is useful as raw materials for cosmetics and food packaging materials due to its ultraviolet ray screening effects.
In general, when a finely-divided titania powder, most particles of which have a size less than 0.1 .mu.m, is incorporated into a resin film or molded product, the film or molded product transmits visible rays and screens ultraviolet rays to protect materials which may be disclored or deteriorated by irradiation with ultraviolet rays. Thus, such finely-divided titania powder has been used in plastic packaging materials for foods and medicines, plastic coating materials for agriculture and horticulture in facilities, cosmetic, etc. Usually, such finely-divided titania powder is produced by thermally hydrolyzing an aqueous titanium sulfate solution to precipitate agglomerated hydrous titanium oxides, neutralizing and washing the agglomerate, peptizing the agglomerate with addition of an acid such as hydrochloric acid or nitric acid to produce a titania sol having a pH of 3 or less, then neutralizing this sol and thereafter subjecting the sol to filtration, washing, drying and grinding (see U.S. Pat. No. 2,448,683).
Generally, a titania sol is stabilized in its dispersion state with acidic reagents such as hydrochloric acid and nitric acid and it shows an acidity of pH 3 or less and so is not suitable for uses in a wide range. In order to remove the acidic reagents and render the titania sol neutral, it can be considered to carry out neutralization-washing, ion exchange, ultrafiltration, etc., but these methods can damage the properties of titania sol such as dispersibility and it is difficult to obtain a neutral titania sol in stable dispersion. Therefore, in general, it is necessary to use an acidic titania sol as a dry powder prepared by subjecting the sol to neutralization, washing, drying and grinding. In this case, however, it is impossible to reproduce the dispersion state such as sol and thus characteristics of finely-divided particles cannot be fully brought about.